One of the major impediments facing the development of in vivo therapeutic and diagnostic applications for monoclonal antibodies in humans is the intrinsic immunogenicity of non-human immunoglobulins. For example, when immunocompetent human patients are administered therapeutic doses of rodent monoclonal antibodies, the patients produce antibodies against the rodent immunoglobulin sequences; these human anti-mouse antibodies (HAMA) neutralize the therapeutic antibodies and can cause acute toxicity. Hence, it is desirable to produce human immunoglobulins that are reactive with specific human antigens that are promising therapeutic and/or diagnostic targets. However, producing human immunoglobulins that bind specifically with human antigens is problematic.
The construction of transgenic animals harboring a functional heterologous (e.g., human) immunoglobulin transgene is one method by which antibodies reactive with self antigens have been produced. However, in order to obtain expression of therapeutically useful antibodies, or hybridoma clones producing such antibodies, the transgenic animal must produce transgenic B cells that are capable of maturing through the B lymphocyte development pathway. While there are a number of examples of transgenic mice capable of maturing through that pathway and thereby undergoing functional V-D-J rearrangement to generate antibodies having both recombinational diversity and junctional diversity, such diversity is limited in comparison to the full genomic potential of any particular species.
In light of such limitations, a clear need exists for methods of efficiently producing heterologous antibodies having increased diversity, e.g. antibodies encoded by genetic sequences of a first species that are produced in a second species, which incorporate an increased fraction of the full genomic heavy and light chain variable region repertoires. There is also a need for a source of B cells which can be used to make hybridomas that produce monoclonal antibodies having such increased diversity for therapeutic or diagnostic use in the particular species for which they are designed.